This invention relates to an index signal generator which generates an index signal. The index signal generator is used for a disk drive that handles a recordable medium, and provides the disk drive with hardware compatibility for the same kind of disk drives. For example, a recordable medium may be a flexible disk and a disk drive may be a flexible disk drive.
In the manner which is well known in the art, the flexible disk drive (which may be hereinafter called “FDD” for short) of the type is a device for carrying out data recording and reproducing operation to and from a disk-shaped magnetic recording medium of the flexible disk (which may be hereinafter called “FD” for short or may be called “a medium”) loaded therein. In addition, such a flexible disk drive is mounted or loaded in a portable electronic equipment such as a laptop personal computer, a notebook-size personal computer, a notebook-size word processor, or the like.
The flexible disk drive of the type comprises a magnetic head for reading/writing data from/to the magnetic recording medium of the flexible disk, a carriage assembly for supporting the magnetic head at a tip thereof with the magnetic head movably along a predetermined radial direction to the flexible disk, a stepping motor for moving the carriage assembly along the predetermined radial direction, and a spindle motor for rotatably driving the magnetic recording medium with the flexible disk held. The spindle motor is one of direct-drive (DD) motors.
In order to control such a flexible disk drive, an FDD control apparatus is already proposed. By way of example, Japanese Patent Application Publication (JP-A) No. H9-97493 discloses, as the FDD control apparatus, one-integrated circuit (IC) chip which incorporates first through third control circuits therein. The first control circuit is a reading/writing (hereinafter called “R/W”) control circuit for controlling reading/writing of data. The second control circuit is a stepping motor (hereinafter called “STP”) control circuit for controlling drive of the stepping motor. The third control circuit is a general controlling (hereinafter called “CTL”) control circuit for controlling whole operation of the flexible disk drive. The CTL control circuit may be called a logic circuit. This IC chip is generally implemented by a metal oxide semiconductor (MOS) IC chip where a number of MOS field effect transistors (FETs) are integrated therein.
The FDD control apparatus comprises not only the one-IC chip but also a spindle motor IC chip for controlling drive of the spindle motor. The spindle motor IC chip is implemented by a bipolar IC chip where a number of bipolar transistors are integrated therein.
Now, flexible disk drives have different specifications due to customers or users. The specification defines, for example, drive select 0 or 1, the presence or absence of special seek function, the presence or absence of an automatic chucking function, a difference of logic for a density out signal, a difference of logic for a mode select signal, 1 M mode 250 kbps or 300 kbps, and so on. If development is made of one-IC chips which individually satisfy the different specification, a number types of one-IC chips must be prepared. In order to avoid this, a one-IC chip having a selectable function circuit is already proposed, for example, in Japanese Patent Application Publication (JP-A) No. H9-97839 wherein all functions satisfying all specifications are preliminarily incorporated therein and one of the functions is selected in accordance with a particular specification.
In the manner which is well known in the art, the flexible disk driven by the flexible disk drive includes a disk-shaped magnetic recording medium accessed by the magnetic head. The magnetic recording medium has a plurality of tracks on a surface thereof that serves as paths for recording data and that are formed in concentric circle along a radial direction. The flexible disk has eighty tracks on one side which include the most outer circumference track (which is named “TR00” and the most inner circumference track (which is named “TR79”). The most outer circumference track TR00 is herein called the most end track.
It is necessary to position the magnetic head at a desired track position in a case where the flexible disk is accessed by the magnetic head in the flexible disk drive. For this purpose, the carriage assembly for supporting the magnetic head at the tip thereof must be positioned. Inasmuch as the stepping motor is used as a driving arrangement for driving the carriage assembly, it is possible for the flexible disk drive to easily carry out the positioning of the carriage assembly. In spite of this, it is necessary for the flexible disk drive to detect only the position of the most end track TR00 in the magnetic recording medium of the flexible disk loaded therein. In order to detect the position of the most end track TR00, the carriage assembly is provided with an interception plate which projects from a base section thereof downwards and a photointerrupter is mounted on a substrate in the vicinity of a main frame opposed to the carriage assembly. For example, see Japanese Patent Application Publication (JP-A) No. H9-91859. That is, it is possible to detect that the magnetic head is laid in the position of the most end track TR00 in the magnetic recording medium of the flexible disk because the interception plate intercepts an optical path in the photointerrupter. Such a track position detecting mechanism is called a “00 sensor” in the art.
In the flexible disk drive where the DD (direct-drive) motor such as a spindle motor is used for rotatably driving the flexible disk, an index signal is generated on the basis of operation in periphery of a rotor of the DD motor. More specifically, a single-pole magnetized magnet (e.g. only a north pole is exposed to the outside) is provided with a peripheral side surface of a disk-shaped casing composing the rotor. Such a magnet is called an index detection magnet. In addition, on a main frame on which a stator of the DD motor and so on are mounted, a main printed wiring board on which a predetermined circuit is formed is disposed. A Hall element is located on the main printed wiring board at a predetermined position corresponding to the outside of the rotor. The Hall element is called an index detection Hall element.
Herein, the Hall element is a semiconductor element applying a Hall effect. The Hall effect is a phenomenon where an electric field occurs in a conductor in a Y-direction perpendicular to both of an X-direction and a Z-direction when the electric current flows in the X-direction in the conductor and when the magnetic field is applied in the Z-direction perpendicular to the X-direction. The electric field caused thereby is a Hall electric field and an output of the Hall element in response thereto is a Hall output.
In addition, Hall elements are used not only as the index detection Hall element but also for detecting a position in the rotor of the spindle motor. Such Hall elements are called position detection Hall elements. A spindle motor using the position detection Hall elements is called a Hall motor.
Although the Hall motor requires three position detection Hall elements, in order to omit their position detection Hall elements, proposal is made to a new motor where states of currents flowing in three-phase coils of the stator are switched on the basis of polarity of an electromotive force induced in one of the three-phase coils that is put into a high-impedance state (e.g. see Japanese Patent Application Publication (JP-A) No. 2000-245125).
In the manner which is described above, in prior art, a single-pole magnetized magnet is used as the index detection magnet. It is difficult to obtain a stable generation timing for the index signal. Accordingly, in order to obtain the stable generation timing for the index signal, the present co-inventors already proposes and files an application to use, as the index detection magnet, a double-pole magnetized magnet (that is, one where a south pole and a north pole are put side by side) (see Japanese Patent Application Publication (JP-A) No. 2001-190055). According to the proposed application, when the pole passing in front of the Hall element changes from the north pole to the south pole, a zero cross point occurs at a Hall output signal. The zero cross point is constant independent of temperature. The index signal is generated based on the zero cross point. It is therefore possible to generate the index signal at stable timing.
A conventional flexible disk drive comprises not only a main frame but also a motor frame for mounting the spindle motor for rotatably driving the medium thereon. This is because it is necessary to form a frequency generation pattern for detecting a rotation speed of the spindle motor on a printed wiring board and it is necessary to mount the printed wiring board on the motor frame. Accordingly, the conventional flexible disk drive is disadvantageous in that it requires a lot of parts and the number of processes for assembling increases. In order to resolve this problem, the present assignee has already proposed a method of controlling the rotation speed of the spindle motor without use of the frequency generation pattern (see Japanese Patent Application Publication (JP-A) No. 2001-178185) and has already proposed a flexible disk drive comprising a motor frame portion for mounting the spindle motor thereon that is constituted by one piece integrated by the main frame (see Japanese Patent Application Publication (JP-A) No. 2001-184774).
In the conventional flexible disk drive, the index detection magnet mounted on the rotor and the index detection Hall element located on the printed wiring board are disposed so that they are apart from each other at a magnetic field detection position by a little distance. The printed wiring board is disposed so as to extend in a direction normal to a rotation axis of the spindle motor. Accordingly, a conventional index detection Hall element necessarily has a magnetic detection surface which is disposed to extend in parallel with a direction of the magnetic field generated by the index detection magnet. Therefore, the conventional index detection Hall element is disadvantageous in that it has a poor sensitive condition for the magnetic field. In order to resolve this problem, the present co-inventors have already proposed a flexible disk drive which is provide with an index detection Hall element having an improved detection sensitive condition for a magnetic field (see Japanese Patent Application Publication (JP-A) No. 2003-85940). According to this proposed flexible disk drive, a motor rotatably driving a flexible disk has a rotor having an external peripheral side surface on which an index detection magnet is mounted. A main circuit board mounts a control circuit for carrying out a driving control of the motor and extends in a direction perpendicular to a rotation axis of the motor. Attached to the main circuit board, a sub circuit board extends in a direction in parallel with the rotation axis of the motor at a position close to the external peripheral side surface of the rotor. Mounted to the sub circuit board, an index detection Hall element has a magnetic field detection surface which is disposed so as to oppose to the external peripheral side surface of the rotor.
In spite of the above-mentioned improvements, a reduction in costs due to a cut of parts and reinforcement of operation stability are desired in the flexible disk drive. This is because, inasmuch as an exclusive index detection magnet and the index detection Hall element are disposed outside the external peripheral side surface of the rotor, miniaturization of the motor due to a cut of a part including the exclusive index detection magnet and the index detection Hall element is desired. In addition, reinforcement of inductance for ensure a back electromotive force in a case of coil detection with the miniaturization is also desired.